1. Field of the Invention
This invention relates generally to self-locking, internally threaded anchoring devices and, more particularly, to threaded insert devices which are suitable for securement to plastic plate-like workpieces.
2. Description of the Prior Art
There are many instances during the fabrication of certain items wherein the use of the standard nut and bolt arrangement is prohibited, and where the thickness of the workpiece is inadequate for threading. For example, such is the case where the fastener must be attached in a blind hole, where the confines of the fabricated structure are such that it is impossible to gain access to the rear side of a bolt hole or where a component has to be attached to a thin sectioned workpiece.
A frequently used type of internally threaded fastener for overcoming this problem has been the conventional collapsible threaded insert or blind self-locking anchoring nut. These conventional threaded insert devices are placed in a hole in the workpiece, which is generally thin gauge metal sheet or metal plate stock and then, with the use of a special tool, are collapsed. Structural components may then be mounted to the workpiece by means of a bolt or screw in conjunction with the threaded insert. Exemplary fasteners of this type are found in U.S. Pat. Nos. 3,304,830 and 3,750,525.
Many improvements have been provided with these inserts to decrease their tendency to rotate within the workpiece when excessive torque is applied to the bolt or screw. Several other improvements have been provided in the application of these threaded insert devices.
In the automotive industry plastic as a material of construction has been more extensively utilized due to weight considerations and total cost of the final product. With the recent emphasis on plastic materials of construction replacing metal, the collapsible threaded insert devices have proved, in some cases, unsatisfactory for particular uses.
When the conventional prior art fastener is used in connection with plastic plate-like workpieces, the collasping of the collapsible sidewall to sandwich the plastic between the head and collapsed sidewall sometimes causes cracking, particularly at the hole edge, due to the lack of ductility of the particular plastic material. Thus, fastening techniques and devices which have been acceptable and desirable for metal workpieces have such disadvantages when used in connection with plastic workpieces.
The invention provides a collapsible threaded fastener insert which is readily collapsible and attachable to plastic workpieces without the disadvantage of cracking and damaging the workpiece.
Further, the invention provides a collapsible threaded insert device for use in plastic material which prevents the rotation of the anchor insert within the workpiece thereby preventing excess torque from impeding the function of the fastener.